fs: improve JSON Unmarshalling for Duration

Enhanced the UnmarshalJSON method for the Duration type to correctly
handle the special string 'off' and ensure large integers are parsed
accurately without floating-point rounding errors. This resolves
issues with setting and removing the MinAge filter through the rclone
rc command.

Fixes #3783

Co-authored-by: Kyle Reynolds <kyle.reynolds@bridgerphotonics.com>

fs/parseduration.go

@@ -1,6 +1,7 @@
 package fs
 
 import (
+	"encoding/json"
 	"fmt"
 	"math"
 	"strconv"
@@ -231,10 +232,26 @@ func (d Duration) Type() string {
 
 // UnmarshalJSON makes sure the value can be parsed as a string or integer in JSON
 func (d *Duration) UnmarshalJSON(in []byte) error {
-	return UnmarshalJSONFlag(in, d, func(i int64) error {
+	// Check if the input is a string value.
+	if len(in) >= 2 && in[0] == '"' && in[len(in)-1] == '"' {
+		strVal := string(in[1 : len(in)-1]) // Remove the quotes
+
+		// Attempt to parse the string as a duration.
+		parsedDuration, err := ParseDuration(strVal)
+		if err != nil {
+			return err
+		}
+		*d = Duration(parsedDuration)
+		return nil
+	}
+	// Handle numeric values.
+	var i int64
+	err := json.Unmarshal(in, &i)
+	if err != nil {
+		return err
+	}
 	*d = Duration(i)
 	return nil
-	})
 }
 
 // Scan implements the fmt.Scanner interface

fs/parseduration_test.go

@@ -214,3 +214,32 @@ func TestParseUnmarshalJSON(t *testing.T) {
 		assert.Equal(t, Duration(test.want), duration, test.in)
 	}
 }
+
+func TestUnmarshalJSON(t *testing.T) {
+	tests := []struct {
+		name    string
+		input   string
+		want    Duration
+		wantErr bool
+	}{
+		{"off string", `"off"`, DurationOff, false},
+		{"max int64", `9223372036854775807`, DurationOff, false},
+		{"duration string", `"1h"`, Duration(time.Hour), false},
+		{"invalid string", `"invalid"`, 0, true},
+		{"negative int", `-1`, Duration(-1), false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var d Duration
+			err := json.Unmarshal([]byte(tt.input), &d)
+			if (err != nil) != tt.wantErr {
+				t.Errorf("UnmarshalJSON() error = %v, wantErr %v", err, tt.wantErr)
+				return
+			}
+			if d != tt.want {
+				t.Errorf("UnmarshalJSON() got = %v, want %v", d, tt.want)
+			}
+		})
+	}
+}